chicken out
US /ˈtʃɪk.ɪn aʊt/
UK /ˈtʃɪk.ɪn aʊt/

1.
acobardarse, echarse para atrás, rajarse
to decide not to do something because you are too frightened
:
•
I was going to try bungee jumping, but I chickened out at the last minute.
Iba a probar el puenting, pero me acobardé en el último minuto.
•
He was going to ask her out, but he chickened out.
Iba a invitarla a salir, pero se acobardó.